Lens mounts serve for precise, mechanical holding of optical single lenses or of a plurality of lenses which are bonded together, otherwise known as cemented groups (referred to hereinafter collectively as round optical components), in exact positions within a lens system, i.e., with a determined spacing and alignment relative to one another. However, particularly in high-power objectives, even slight positional deviations of individual lenses of the lens system can lead to unwanted system errors.
In objectives in which round optical components without mounts are arranged relative to one another directly inside an objective tube, also known as tube or nested-cell mount, the objective tube together with the means by which a round optical component is held therein can be considered as a lens mount within the meaning of the invention.
However, the round optical components can also be mounted directly in individual auxiliary mounts with mount rings, and the auxiliary mounts can be arranged relative to one another, e.g., inside a shared housing which can also be an objective tube. An auxiliary mount of this kind can also be a lens mount within the meaning of the invention.
Frequently, a round optical component is axially fixed within an objective tube or mount ring, both of which are referred to hereinafter as mount ring, in that the optical component is placed with one end face against an annular edge support formed in the mount ring and a screw ring which is screwed together with the mount ring is adjusted to the other end face.
In this regard, in the textbook “Device Construction [Gerätekonstruktion]” (Werner Krause, ed., VEB Verlag Technik Berlin, 1st edition (1982), page 482, last paragraph, to top of page 483), it is stated under the heading “Mount with screw ring, screw cap” that mounting with screw rings, especially with slotted screw rings, is the commonest way of securing round optical components. In all of the arrangements shown in this reference, the round optical components contact an edge support of a mount ring by one end face annularly in a planar manner, while there is annular line contact between the screw ring and the other end face of the optical component.
The advantage in this type of mounting of round optical components resides in the simple assembly in which the optical component is placed against an edge region of a mount ring axially in a frictionally engaging manner and in the simple production of the mount parts required for mounting, namely, a mount ring and a screw ring. This results in a cementless, economical lens mount.
It is disadvantageous that stresses are introduced into the optical component which grow as the tightening force of the screw ring increases toward the mount ring. This results in birefringences in the optical component which negatively affect its imaging quality.
Beyond this, this type of lens mount is not temperature-compensated so that temperature fluctuations lead to undefined radial changes in position of the optical component in the mount ring because of the different coefficients of expansion of the material of the optical component and mount parts. Therefore, it is not suitable for high-power objectives which must maintain consistent imaging quality over a given temperature range.
Further, a lens mount with a three-point contact on both sides and a slotted screw ring is known from the above-cited textbook.
A self-centering holder for a mounted lens is described in Laid Open Application DE 196 23 418 A1. The lens lies directly on the lens mount at three contact points and is nondetachably connected to the lens mount by adhesive. The mounted lens is elastically supported in a sleeve to absorb radially acting forces. Further steps for axial support are not described.
Laid Open Application DE 100 30 004 A1 describes an apparatus for supporting an optical element. The support takes place at polished support points in the edge region of the optical element on three bearing bodies with spherical surface. For purposes of exact positioning and reproducible support of the optical element, one of the three support points is planar, one is grooved and one is conical. The support on the bearing bodies is secured by means of securing devices which contact the opposite side of the support points without force.
In an optical holder described in Laid Open Application JP 2008 261 985 A, the axial support of the optics is effected via three bearing elements which are received at an axial surface of the holder so as to be spaced apart by 120°. The bearing elements are balls having a flattened location on which the optics lie. The balls are supported in the holder at the edges of bores which are smaller than the ball diameter. The optics are secured in the same manner, the flattened balls being arranged in bores of a respective holding element which is screwed to the holder and secured in position. The clamping force between two respective bearing elements is adjusted by the screwed-on holding element.
A low-stress optics mount having a mount ring and a spring ring is known from Laid Open Application DE 103 42 269 A1. The radial mounting of the optics is carried out with no clearance or pressing at an inner lateral surface of the mount ring. The axial mounting is carried out at three axial stops of the mount ring which are spaced apart at 120° so as to be operative only at three points. The optics are secured in the mount ring with the three-point spring ring which rests on the optics in the edge region by three pressure surfaces opposite the axial stops. The spring force is adjustable.